A method for combusting fuels in a substantially conically shaped curtain

ABSTRACT

A device and method for improving the combustion of fuels which emerge from the orifice of a burner nozzle in the form of a conically shaped fuel curtain, around which and coaxial with is a connecting envelope of combustion air. Extending coaxially with the main burner tube are further tubes which form air passages. The further tubes are provided at the ends thereof adjacent the fuel nozzle with air nozzle means which give the air a determined direction of flow relative to the radial plane, thereby creating a subpressure externally of the fuel and air cones, whereupon the cones are drawn rearwardly and outwardly with respect to the burner nozzle tip.

[ Sept. 11, 1973 METHOD FOR COMBUSTING FUELS IN A SUBSTANTIALLY CONICALLY SHAPED (IURTAIN Inventor:

Martti Ilmari Kiilhi, Stenhamra, Sweden R. Collin Consulting AB, Stockholm, Sweden Filed: Mar. 23, 1971 Appl. No.: 127,228

Assignee:

Foreign Application Priority Data Mar. 24, 1970 Sweden 4010/70 References c1160 UNITED STATES PATENTS 12/1964 Schmidtet a1 431/157 x 9/1966 Ward 431/8 X 4/1962 Johnson 431/9 X 3,576,384 4 1971 P661611 239 424 2,986,206 5 1961 1366181119. 431/9 2,515,845 7/1950 Van Den Busschem, 431/9 836,219 11/1906 Schutz 431 9 FOREIGN PATENTS OR APPLICATIONS 1,297,465 5 1962 France 239 424 Primary Examiner-Meyer Perlin Assistant Examiner-William C. Anderson Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT A device and method for improving the combustion of fuels which emerge from the orifice of a burner nozzle in the form of a conically shaped fuel curtain, around which and coaxial with is a connecting envelope of combustion air. Extending coaxially with the main burner tube are further tubes which form air passages. The further tubes are provided at the ends thereof adjacent the fuel nozzle with air nozzle means which give the air a determined direction of flow relative to the radial plane, thereby creating a subpressure externally of the fuel and air cones, whereupon the cones are drawn rearwardly and outwardly with respect to the burner nozzle tip.

10 Claims, 10 Drawing Figures PATENTEI] SEP! 1 I973 SHEET 1 UP '3 PATENTEU-SEPI Hm sum 2 [IF 3 v PATENTEDSEH m sum afar 3 METHOD FOR COMBUSTING FUELS IN A SUBSTANTIALLY CONICALLY SHAPED CURTAIN The present invention relates to a method for combusting fuels which are ejected from an orifice in a manner to form a substantially conically shaped curtain of fuel which is mixed with an envelope of combustion air located substantially coaxial with the fuel curtain.

Injury to the environment as a result of impurities discharged to atmosphere from plants fired with fossil solid or liquid fuels is becoming more and more serious. With, for example, oil fired systems used to heat dwellings, produce electrical energy etc. the waste gases normally contain, inter alia, soot, carbon monoxide, sulphur oxides and/or nitorgen oxides as a result of unsatisfactory combustion. Large systems of present day construction are normally provided with filter devices which separate, although not all, at least a major portion of the soot. On the other hand, the harmful nitrogen and sulphur dioxides pass through the filer devices and are discharged to atmosphere. In the case of housing developments in which each building is provided with a separateboiler system, it has normally not been possible for reasons of economy to equip each system with such filter devices and other contaminant separating devices. Consequently, the only possibility of solving air contamination problems in such areas is to improve the actual process of combustion, and it is therefore desirable to obtain a combustion process which is so complete that neither soot nor any other product of combustion harmful to the environment can be formed. When combustion is complete a blue flame is obtained and consequently efforts have hitherto been directed towards effecting the combustion processes in a manner whereby a yellow flame, which indicates that free carbon is present, is eliminated to the highest extent possible. 7

Consequently, in order to improve the combustion process in this respect and to reduce the risk of soot formation it has been necessary to experiment in practice with considerable flow velocities, both with respect to the fuel and to the air of combustion supplied to the burner. The high velocities, however, considerably impair the duration and strength of the flame, with the accompanying risk of extinguishing the same. Moreover, a troublesome high sound level is obtained. In spite of considerable efforts and steps, no burner constructions have hitherto been proposed which, particularly with respect to small systems,'can be said to solve completely the problem on which the invention is based, namely that of effecting the process of combustion more economically and so completely'that soot development and the formation of destructive chemical substances is eliminated. With soot-free combustion it is possible to effect the process of combustion stoichiometrically, which has a favourable effect on the fonnation of sulphur and nitrogen oxides. Thus, S0, is

formed instead of S0,, which reduces the corrosion problems occurring as a result of the formation of sulphuric acid with the moisture contained in the waste gases.

The problems prevailing in the present connection with small and medium sized burners have been eliminated by means .of the present invention, which is mainly. characterized in that a condition for subpressure is maintained outside the curtain of fuel and the combustion air envelope located around the axis of the fuel cone, said subpressure condition holding the combustion zone displaced rearwardly and concentrating the combustion zone around the axis of the fuel cone.

The invention also relates to a device for carrying out the method and is substantially characterized in that arranged in a ring around the axis of the burner cone and externally of the fuel curtain and the combustion air envelope are members adapted to cause the atmosphere externally of the combustion air envelope and the fuel curtain to move outwardly from the cone axis to maintain a condition of subpressure which holds the combustion zone rearwardly displaced and concentrates said combustion zone around the cone axis.

The invention will now be described in more detail with reference to a number of embodiments thereof diagrammatically illustrated in the accompanying drawing, further features of the invention being disclosed in conjunction therewith.

FIG. 1 illustrates in perspective and in partially broken away view a basic condition of a substantially coneshaped curtain of fuel issuing from the nozzle orifice of a burner and the cone of combustion air located coaxial with the fuel curtain.

FIG. 2 illustrates separately and in perspective how the outer surface of the fuel cone is influenced by a subpressure, resulting in an increased cone angle.

FIG. 3 illustrates, also in perspective, a fuel cone and a connecting cone of combustion air subjected to a subpressure on the outer surfaces thereof.

FIG. 4 shows in perspective and partly in longitudinal section an embodiment of a burner constructed in. ac-

cordance with the invention and provided with means which cause the atmosphere outside the cones to move to create and maintain the necessary subpressure.

FIG. 5 illustrates how air is directed by positively guiding the same at suitable preferred and critical angles to the radial plane of the burner.

FIG. 6 illustrates the possibility of causing the positively guided air to rotate around the burner axis of a burner of the type illustrated in FIG. 4 for example.

FIG. 7 illustrates in longitudinal section a modified burner in which the desired subpressure is created by means of an ejector action. I

FIG. 8 is an axial partial sectional view of a further modified burner construction with which the combustion zone is displaced rearwardly to extreme limits.

FIG. 9 illustrates a modified embodiment of the structure illustrated in FIG. 6.

FIG. 10 is an axial section of a further embodiment of the invention.

In accordance with the main principle of the invention, FIG. 1 illustrates the basic condition of a fuel spray issuing from a fuel orifice 10 of a conventional fuel nozzle 11. The emerging fuel forms a conical film 12 which is atomized into fine droplets. The fuel cone 12 is surrounded by a conical envelope 13 of combustion air which emerges through a constriction 14 in a casing or the like 15 surrounding the fuel nozzle ll. In practice, the cones act upon each other and the surrounding atmosphere, but for the sake of simplicity the cones are shown in a theoretical condition and their influence on each other and the surroundings has been ignored. Although not shown in FIG. 1, the fuel cone and/or the air cone are capable of rotating around their respective cone axes, either in the same direction or in opposite directions and at the same or different speeds. In practice, however, the atomized fuel is mixed with the air of combustion, and the subpressure created within the cones, as a result of the flow, tends to draw the fuel and the air of combustion rogether. When igniting the fuel air mixture by appropriate ignition means (not shown), a relatively long, yellow flame is obtained, which indicates that free carbon is present, because the temperature increase of the fuel air mixture is too slow. The final products obtained during the process of combustion consist of, inter alia, S S0 elemental carbon, i.e., soot and nitrogen oxides, which are deleterious to the environment, as indicated in the aforegoing.

FIG. 2 illustrates the same fuel nozzle 1i. as that illustrated in FIG. 1, the casing having been removed and the conical air envelope 13 excluded. The Figure also illustrates in chain lines the initial position of the fuel cone. The Figure illustrates diagrammatically an example of how, in accordance with the invention, the atmosphere outside the fuel cone 12 is caused to move outwardly from the burner axis in the direction of arrows 16. In this instance, it is presumed that arranged concentrically with the axis is an annular gap or ring of orifices which is or are connected to a source of subpressure, e.g. the illustrated suction fan 17 whose suction inlet opening is identified with the reference numeral 18 and the ejection outlet opening with the reference numeral 119. The air drawn into the fan is discharged through the opening 19 externally of the burner. The resulting movement of the atmosphere in the direction of arrows 16 in the zone externally of the fuel cone 12 creates a subpressure which results in the widening of the fuel cone, which thus takes the shape of a bowl 20, as illustrated in the Figure, and the cone angle of which is also considerably increased.

The helical arrow Zll indicates a flow line, which shows that in this instance the fuel bowl 20 rotates around its axis, although it is not always necessary for the fuel bowl to rotate. Movement of the fuel bowl can be accomplished in a known manner, for example by arranging tengentially directed grooves inside the nozzle.

FIG. 3 illustrates diagrammatically how the fuel cone and the air cone are actuated in the manner described with reference to FIG. 2. FIG. 3 thus shows the nozzle orifice 10, the nozzle 11, the casing 15, the restriction 14, the initial fuel cone and air cone i2 and 13 respectively and the fuel bowl 20. Also illustrated in the Figure is a bowl-shaped envelope of combustion air 22 which is located around the fuel bowl 20 coaxialiy therewith. Indicated in respective bowls by helical arrows 21 and 23 are flow lines which show how the bowls may rotate. The arrows 16 shown in FIG. 2 are also shown in FIG. 3 and represent appropriate directions of movement for the atmosphere present during removal by suction of the atmosphere from the zone located substantially within the base of the arrows and which is of particular interest in connection with the invention. The Figure also illustrates how the fuel cone 12 and the combustion air cone 13 have been substantially widened. This'widening of the two cones is caused by the subpressure created in the zone nearest the fuel opening as a result of air flowing out through the restriction l4 and of the subpressure which in turn is created around the cylindrical surface of the envelope of combustion air in the region radially outside the restriction 14. By widening the cone angles, the bowsl 2% and 22 are caused to coincide, whereupon a concentrated mixture of air and fuel is obtained which when ignited gives a relatively stable combustion zone. When the subpressure is increased, the combustion zone is moved rearwardly towards the burner nozzle and is concentrated radially inwardly. Combustion is effected more rapidly in this combustion zone than with the example described with reference to FIG. 1. In this way, a more rapid increase in temperature is obtained, resulting in the suppression of soot formation and the formation of other final products harmful to the environment.

While FIGS. 1-3 are intended to illustrate the principle of the method according to the invention, FIGS. 4-10 illustrate more concrete devices for putting the method of the invention into effect, further developments of the method being described with reference to these Figures.

The method according to the invention for creating a region of subpressure outside the respective fuel and combustion air cones has, in the aforegoing, only been described and illustrated in principle, with reference to FIGS. 1-3. The source or means for causing the atmosphere in the zones in question to move outwardly from the common cone axis has been exemplified in the form of a suction fan or the like, which, as will be understood, only represents an extremely elementary embodiment of the method according to the invention. Furthermore, mention has been made of a method by which the air flow paths are given a specific direction without the means for carrying out the method having been described in detail.

It is particularly advantageous to the method of the present invention if the combustion air and/or the fuel mist can be caused to rotate. Such rotation contributes to a more effective mixture of the fuel mist with the combustion air. One example of a burner by means of which this development of the method according to the invention can be carried out is illustrated in FIG. 4, in

i which the reference numeral 24 indicates a body surrounding the fuel nozzle 25 and widening in a direction towards the discharge end of the burner. The body 24 is extended with a tubular portion 26, which simultaneously forms a passage for the fuel and an attachment means for a number of helically arranged guide vanes 27. The body 24 and its stem 26 are encircled by two co-axial tubes, of which the inner is identified with the reference numeral 28 and the outer with the reference numeral 29. The tubes 28 and 29 are provided attheir ends located around the nozzle 25 with flanges 30 and 31. Between the body 241 and its stem 26 and the inner tube 28 there is defined a flow passage 32 for air of combustion, which is given a rotary movement by the guide vanes 27, as indicated by the arrows 33. As will be seen from the Figure, the flow passage has a restriction 34, provided by the embodiment of the body 24. As a result of this restriction, the combustion air is subjected to an ejector action. Moreover, formed between the tubes 28 and 29 is a relatively narrow, angular passage through which air is forced to flow in the direction of arrows 36 out through an annular gap 37 located between the two flanges 3b and 31.

As illustrated in the Figure, the fuel issues from the nozzle opening 35 to form a bowl-shaped curtain of fuel identified in FIG. 3 with the reference numeral 20.

combustion air bowl rotates around its axis relative to the fuel bowl 20, as shown by the arrows 33. In this way, an intensive mixture of the fuel and the air is obtained, together with a rapid combustion, as described with reference to FIG. 3. The combustion, however, can be further considerably improved by intensifying recirculation of hot smoke gases and still unburned fuel-air mixture. FIG. 4 illustrates amethod of causing such recirculation by eddying the atmosphere around the zone of combustion. As will be seen from the Figure, the positively directed air emerging through the annular gap 37 in the direction of arrows 36 causes, by ejector action, the air nearest the gap 37 to rotate and form eddies 38, which lie in the form of a ring around the flange 30. In turn, the eddy movement together with the gas movement in the zone of combustion induces a very intensive eddy movement, identified by the arrow 3!, whereby hot smoke gases are recirculated back to the beginning of the combustion zone. The recirculated hot smoke gases will further increase the temperature in the combustion zone, so that combustion becomes extremely intensive and is therewith also concentrated to a relatively narrow region around the burner axis, simulatneously as the combustion zone is moved closer to the burner orifice. A particularly important factor correlated with the withdrawal of the combustion zone is the flow of air through the restriction 34 around the body 24, this flowcausing, by ejector action, a region of subpressure to be created in front of the body 24 around the fuel nozzle 35. It should be observed that occurring simultaneously within the two, now coinciding bowls 20 and 22 is arecirculation of hot smoke gases which is directed towards the fuel orifice. Naturally, these hot combustion gases contribute in the aforedescribed manner to intensify the combustion in the combustion zone.

It has been discovered in connection with the invention that the angle to the radial plane for the positively directed air flow from the gap between the flanges 30 and 31 is critical or should at least be maintained within certain suitable angle regions in order for a reasonable combustion result to be obtained. In the diagrammatic view of FIG. 5 the two tubes 28 and 29 are shown with their flanges 31 and 30 directed at a negative angle of 20 to the radial plane, which is represented by the line 40. This angle of 20 is applied in the embodiment illustrated in FIG. 4. Experiments have shown, however, that it is possible to direct thegas flow positively at an angle of between and 60 tothe radial plane, as is diagrammatically illustrated in FIG. 5. Particularly suitable angular areas are those which extend at +5 to 30" to the radial plane and whichextend outwardly from the nozzle axis in accordance with the invention.

It can also be to advantage at the same time to direct the gas flow positively at an angle to the radius of the aformentioned radial plane, and by way of example reference is made to the perspective, cut away view of the burner illustrated in FIG. 6. The arrows 41, which illustrate the positively directed gas flow, are thus in this instance directed at an angle to lines extending perpendicularly to the axis of the burner nozzle. Such positively directed movement can be produced, for example, by causing the air advanced between the tubes 28 and 29 to move in a helical path and to permit the air to emerge in the direction of arrows 41. In accordance with another alternative, the inner edge surfaces of the flanges. 30 and 31 in the gap 37 can be provided with vane like members or the gap can be replaced with a ring of openings 63 which have a determined direction of orientation and which positively guide the air to flow at the desired angle to the lines extending perpendicularly to the axis of the burner nozzle, as shown in FIG. 9.

FIG. 7 illustrates diagrammatically a further embodiment of a burner in which the flow passage for the combustion air is incorporated in an ejector means arranged to lower the pressure in the area around the burner tip externally of the fuel air bowl. In FIG. 7, the reference numeral 42 identifies the fuel nozzle proper, which is surrounded by a body 43, past the edge surface 44 of which combustion air flows in the direction of the arrows 45 through an encircling tube 46, which terminates approximately level with the edge surface 44 of the body 43. Arranged coaxially with the tube 46 is an outer tube 47, an annular flow gap being formed in which air flows in the direction of arrows 48. Positioned at the end of the tube 47 is a ring of combined support and distance means which support an annular, outlet member, generally indicated at 49, at such a distance from the end of the tube 47 that an annular opening 50 is formed between the end of the tube 47 and the outlet member 49. By cooperation between the air flows in the inner tube 46 and in the gap between the tube and the outer tube 47, eddies 51 are created in the region around the burner tip and externally of the fuelair bowl, the eddies being formed as a result of a subpressure formed externally of the gap 50 by ejector action. The eddies substantially comprise recirculated smoke gas entrained from the contact zone between the eddies 51 and the cylindrical surface of the bowlshaped envelope of the combustion zone represented by the arrows 52. As shown in the Figure, a central recirculation is also obtained within the combustion zone, as illustrated by the looped arrows 53. In this way there is obtained a recirculation of combustion gases in a direction towards the innermost point of the fuel bowl, whereby the fuel mist is quickly heated and rapid combustion is obtained as a result thereof. The Figure also shows by way of example the two terminals X and Y of an arbitrarily selected fuel igntion means.

FIG. 8 illustrated one half of a further modified burner construction according to the invention, in which the central body 43 illustrated in FIG. 7 is shown. With the modified construction, an inner tube 54 terminates at a certain distance behind the edge surface 44 of the body 43. An outer tube 55 having an annular or ring-shaped ejector 56 surrounds the tube 54 with an intermediate annular gap 57 and terminates at a certain distance in front of the end surface of the body 43. Combustion air flows in the direction of arrow 59 between the body 43 and the inner tube 54 through a constriction S8 and past the end of the tube 54, where the air is entrained raidally outwardly by the air emerging at a higher velocity from the gap 57. The two air flows together then give rise to an ejector action when passing the ejector 56, so that a recirculation eddy, indicated by the arrow 60, is created similarly to the eddy 51 in FIG. 7 with the same effect.

The radially outwardly deflected flow of combustion air, flowing through the constriction 58 in the direction of arrows 59, creates a subpressure in front of the end surface of the body 53 and around its end surface 44.- This region of subpressure contributes to drawing the .fuel film 61 outwardly and deflects the same rearwardly, whereupon the film 61 is surprisingly and effectively atomized into an extremely fine mist which is drawn behind the edge 44 and mixed with the combustion air. Under ideal conditions, the combustion zone will then obtain a profile such as that represented by the dash line 62.

H6. illustrates another embodiment of the invention in which is embodied a number of gaps or passages for positively directing the air flows at different angles to the aforementioned lines extending perpendicularly to the axis of the nozzle. In the Figure, the reference numeral 64 identifies a central tube which bears at one end thereof a fuel nozzle 65. Extending coaxially with the tube 64 are two tubes 66 and 67, these being defined between the tubes air through flow passages 68 and 69. The tube 64 is provided in the vicinity of the burner nozzle 65 with guide surfaces 70 which together with guide surfaces 71 on the tube 66 give the flow of air a direction determined by the gap. The tube 66 is also provided with guide surfaces which together with guide surfaces 73 on the tube 67 direct the air flow in a direction different to the first mentioned air flow.

it will be understood that although only two gaps have been shown further gaps may be arranged and that their configuration may be so selected that the air passing therethrough may be made to flow in any desired direction relative to the radial plane.

The invention is not restricted to the illustrated and described embodiment but can be modified within the scope of the following claims.

What we claim is:

1. A method of combusting fuel comprises forcing said fuel through an orifice adapted to produce a conically shaped fuel curtain; forcing combustion air through a substantially annular flow-through area located coaxially with said orifice, directing said combustion air away from the axis of the fuel cone to form a substantially conical or bowl shaped curtain concentric with and exterior to said fuel cone; maintaining the pressure used to force said combustion air at a sufficiently high level to create a sub-atmospheric pressure zone between said combustion air curtain and said fuel cone whereby said fuel cone angle is increased and said fuel is admixed with said combustion air in a combustion zone; igniting said admixture and mainting said combustion zone during combustion.

2. A method according to claim 1 including continuously withdrawing the atmosphere by suction to influence the pressure conditions at the air curtain.

3. A method according to claim 1 including causing the atmosphere adjacent the air curtain to move in a substantially toroidal shaped pattern of eddy current to influene the pressure conditions at the air curtain.

4. A method according to claim 3, wherein said at mosphere is activated by means of a positively propelled and directed gas flow to produce said toroidal shaped pattern of eddy currents.

5. A method according to claim 2, wherein said pressure condition is maintained by the combination of suction and positive propulsion and direction of a gas flow.

6. A method according to claim 2, in which the flow of gas is directed at an angle of between +10 and 60 to the radial plane of the axis and in a direction away from said axis.

7. A method according to claim 2, in which the flow of gas is directed at an angle of between +5 to 30 to the radial plane of the axis and in a direction away from said axis.

8. A method according to claim 2, in which the flow of gas is directed at an angle of approximately 20 to the radial plane of the axis and in a direction away from said axis.

9. A method according to claim 8, wherein said gas flow is also directed at an angle to the radius of the radial plane.

10. A method according to claim 21, wherein said combustion zone is held withdrawn rearwardly beyond the fuel orifice by maintaining sub-atmospheric condition behind said orifice.

t IF 

1. A method of combusting fuel comprises forcing said fuel through an orifice adapted to produce a conically shaped fuel curtain; forcing combustion air through a substantially annular flow-through area located coaxially with said orifice, directing said combustion air away from the axis of the fuel cone to form a substantially conical or bowl shaped curtain concentric with and exterior to said fuel cone; maintaining the pressure used to force said combustion air at a sufficiently high level to create a sub-atmospheric pressure zone between said combustion air curtain and said fuel cone whereby said fuel cone angle is increased and said fuel is admixed with said combustion air in a combustion zone; igniting said admixture and mainting said combustion zone during combustion.
 2. A method according to claim 1 including continuously withdrawing the atmosphere by suction to influence the pressure conditions at the air curtain.
 3. A method according to claim 1 including causing the atmosphere adjacent the air curtain to move in a substantially toroidal shaped pattern of eddy current to influene the pressure conditions at the air curtain.
 4. A method according to claim 3, wherein said atmosphere is activated by means of a positively propelled and directed gas flow to produce said toroidal shaped pattern of eddy currents.
 5. A method according to claim 2, wherein said pressure condition is maintained by the combination of suction and positive propulsion and direction of a gas flow.
 6. A method according to claim 2, in which the flow of gas is directed at an angle of between +10* and -60* to the radial plane of the axis and in a direction away from said axis.
 7. A method according to claim 2, in which the flow of gas is directed at an angle of between +5* to -30* to the radial plane of the axis and in a direction away from said axis.
 8. A method according to claim 2, in which the flow of gas is directed at an angle of approximately -20* to the radial plane of the axis and in a direction away from said axis.
 9. A method according to claim 8, wherein said gas flow is also directed at an angle to the radius of the radial plane.
 10. A method according to claim 21, wherein said combustion zone is held withdrawn rearwardly beyond the fuel orifice by maintaining sub-atmospheric condition behind said orifice. 